Switch

ABSTRACT

A switch comprises a housing having fixed switching contacts and a slidable carriage which is movable by a switch-on spring. The switch-on spring can be locked in place. A slide having moving switching contacts is also provided and is movable by a switchoff spring, which can also be locked. The slide having the moving contacts is arranged for sliding movement in the carriage. The springs are consecutively unlocked by a trigger mechanism moving twice in the same direction.

0 tinned States Patent 1 3,7353% Kreutzelman et al. 1 May 22, 1973 SWHTCH [56] References Cited [75] Inventors: Harm Kreutzelman; Laurentius UNITED STATES PATENTS Maria Verhoeven, both of Emmasingel Eindhoven, Netherlands 1,559,329 10/1925 Lemlyn ..200/78 [73] Assignee: U.S. Philips Corporation, New pn-mwy Examiner David Smith, JL

Attorney-Frank R. Trifari [22] Filed: Nov. 11, 1971 21 Appl. No.: 197,861 [57] ABSTRACT A switch comprises a housing having fixed switching [30] Foreign Application Priority Data contacts and a slidable carriage which is movable by a switch-on spring. The switch-on spring can be locked NOV. 21, 1970 Netherlands ..7017069 i place. A Slide having moving Switching contacts is also provided and is movable by a switch-off spring, (gl. which can also be locked The Slide having the moving [58] Fie'ld 77 78 160 contacts is arranged for sliding movement in the carriage. The springs are consecutively unlocked by a trigger mechanism moving twice in the same direction.

18 Claims, 6 Drawing Figures 1S3 13 1517 QMZi VA e 45 HF I n an l I (\if 9 :1

PATEN TED MAY 2 2 I975 SHEET 3 OF 3 M 4 w v M ww y w 9 2 ivy- A Agent swrrcn The invention relates to a switch which may be switched on and off with the aid of a switch-on spring and a switch-off spring. The springs can both be tensioned and locked in the tensioned state in one movement. An intermediate piece is provided which can be moved by the switch-on spring while the switch-off spring remains tensioned. Such a switch is known from German Pat. specification 1,049,956, and has the property that the actual switching on and switching off can be effected at a very fast speed without a large force being required for the switching operations. In fact, the required energy is stored in the tensioned springs. This property is very useful for switches which are to be automatically operated for example by means of a rotating cam wheel and in which it is important that both switching on and switching off is effected at an accurately determined position of the cam wheel. Such accuracy may best be achieved by providing a follower lever pressed against a cam wheel whose profile has two consecutive abrupt transitions. The first transition switches on the switch when the follower lever passes and the second transition switches off the switch. For smooth movements of the follower lever it is desired that the follower lever moves in the same direction for both transitions, namely the direction in which it is urged. This means that for switching on and switching off only one operating member should be present which is moved in the same direction for both switching operations.

The object of the present invention is to provide a switch structure which satisfies the above requirements and which can be manufactured with comparatively few components. According to the invention this object is achieved in that the intermediate piece consists of a carriage adapted to reciprocate in a housing having fixed switching contacts. A slide having movable switching contacts is joumalled to reciprocate in said carriage. The switch-on spring is arranged to act on the housing and the carriage and the switch-off spring acts on the carriage and the slide. The springs are unlocked with the aid of a trigger mechanism joumalled in the housing and are movable in at least two consecutivestages into the same direction. The trigger mechanism unlocks the switch-on spring during the first-stage so that the carriage, taking along the slide, shifts relative to the housing, and unlocks the switch-off spring during the second stage so that the slide shifts relative to the carriage. The locking mechanism for the switch-off spring may be constituted by a switch-off lever journalled in the carriage and having at least two legs the first leg of which can co-operate with a recess in the slide for the purpose of locking, while the second leg can co-operate with the trigger mechanism for the purpose of unlocking. The locking mechanism for the switch-on spring may be constituted by a switch-on pawl joumalled in the carriage, which pawl can engage a groove in a component of the trigger mechanism for the purpose of locking. A simple and reliable structure for the trigger mechanism consists of a trigger having three legs the first leg of which is connected to a driving mechanism while'the second and third legs can cooperate with the switch-on pawl and the switch-off lever, respectively. It is sometimes desirable to be able to tension and lock the springs while the trigger mechanism is not in the position in which it locks the switchon spring. According to a modification of the invention this is achieved in that an auxiliary pawl is joumalled in the carriage, which pawl engages a groove in the housing if the springs are tensioned while the trigger mechanism is in a position in which locking by means of the switch-on lever does not occur and thereby locks the switchon spring until the trigger mechanism can take over the locking operation.

In some cases it is also desirable to be able to switch off the switch before this is effected by the trigger mechanism. According to a further modification of the invention this can be accomplished by providing the switch-off lever with a third leg which can be manually moved in such a manner that the switch-off spring is unlocked thereby independently of the position of the trigger mechanism.

In order that the invention may be readily carried into effect, some embodiments thereof will now be described in detail by way of example with reference to the accompanying diagrammatic drawings in which:

FIGS. l to 4 show in a longitudinal section an embodiment of a switch according to the invention in four different operating conditions FIG. 5 shows the principle of the operation of a possible driving mechanism for the switch according to the invention and FIG. 6 shows partly in a cross-section a practical embodiment of such a driving mechanism.

The switch shown in FIGS. 1 to 4 consists of a housing l in which fixed switching contacts 3 are secured. A carriage 5 is joumalled to reciprocate in the housing 1. A slide 7 is likewise joumalled to reciprocate in the carriage 5, which slide supports movable switching contacts 9 which with the switch being switched on are urged by springs 11 against the fixed switching contacts 3 and then, for example, electrically connect two fixed switching contacts 3 together.

Carriage 5 has a portion 13 which protrudes from the housing 1 and which is provided with a flange l5 engaging a switch-on springvl7 which at its other end acts on the housing 1 and exerts a force to the left onthe carriage 5 in FIGS. 1 to 4. The switch-on spring 17 may be brought to the tensioned state shown in FIG. 1 by depressing a button 19. The switch-on spring 17 is locked in this position by a switch-on pawl 21 pivoted in the carriage 5 about a shaft 20 and co-operating with a trigger mechanism which consists of a trigger lever 23 having three legs and being pivoted in housing 1 about a shaft 22, the first leg 25 being connected to a driving mechanism 27. The operation of this driving mechanism will be explained hereinafter with reference to FIG. 5. For a satisfactory understanding of the switch it is only important that the driving mechanism 27 can rotate the leg 25 and hence the trigger lever 23 counter-clockwise in two stages starting from the position shown in FIG. 1 (see FIGS. 2 and 3) and subsequently gradually clockwise until the starting position is reached again. In the position shown in FIG. 1 of the switch the switch-on pawl 21 is urged into a recess in the second leg 29 of the trigger lever 23 by means of a leaf spring 28 connected to the carriage 5 so that the carriage 5 is prevented from sliding to the left.

When the trigger lever 23 makes one step counterclockwise, the switch-on pawl 21 is released from the second leg 29 so that the carriage 5 slides to the left and the state of FIG. 2 is reached. The slide 7 is taken along to the left by the carriage 5 so that the switch is switched on. The connection required for slide 7 to be taken along by carriage is constituted by a switch-off lever 33 pivoted in the slide about a shaft 31 and locking a switch-off spring 35 which acts on the carriage 5 and the slide 7. The switch-off spring 35 is compressed in FIG. 2 and exerts a force directed to the right on the slide 7. The slide 7 is prevented from shifting to the right relative to the carriage 5 by a first leg 37 of the switch-off lever 33 which has a cam 39 engaging a recess 41 in slide 7. A spring 45 which urges the cam 39 into the recess 41 is provided between the second leg 43 of the switch-off lever 33 and the carriage 5. The second leg 43 of the switch-off lever 33 may be pressed downwards against the force of spring 45 by the third leg 47 of the trigger lever 23 so that the cam 39 is lifted from the recess 41. As a result slide 7 is pressed to the right by spring 35 which results in the switch being switched off. This is effected when the trigger lever 23 has made the second step counterclockwise and this leads to the state of FIG. 3.

The most common procedure is for the driving mechanism 27 to gradually rotate the trigger lever 23 clockwise back to the starting position of FIG. 1 whereafter the switch-on spring 17 and the switch-off spring 35 can again be tensioned and locked by depressing button 19. The carriage 5 then slides to the right so that the switch-on spring 17 is tensioned while the slide 7 is retained because the movable contacts 9 abut against uprights 49 (partly shown in broken lines) of the housing 1. As a result the switch-off spring 35 is also tensioned.

It is sometimes desirable to tension the springs 17 and 35 before the trigger lever 23 has returned to its starting position. Such a situation is shown in FIG. 4. Locking of the switch-off spring 35 does not provide any problems because the third leg 47 in the given position of the trigger lever 23 is slanted downwards and hence does not press the leg 43 of switch-off lever 33 downwards after the switch-off lever has shifted to the right together with carriage 5. Locking of the switch-on spring 17 by trigger lever 23 is, however, only possible after the trigger lever has come close to the starting position of FIG. 1. To enable the switch-on spring 17 to be locked in the meantime, an auxiliary pawl 51 is provided which is pivotable about the same shaft as the switch-on pawl 21. In the position shown in FIG. 4 the auxiliary pawl 51 is urged into a recess 55, provided in the housing 1, by means of a leaf spring 53 connected to the carriage 5. The end of the second leg 29 of trigger lever 23 extends so far that this leg lifts the auxiliary pawl 51 from the recess 55 when the trigger lever is rotated to its starting position. Then, however, the leg 29 has come to such a low position that the recess accommodated therein can mesh with the switch-on pawl 21. At the instant when the auxiliary pawl 51 unlocks the switch-on spring 17, the switch-on pawl 21 takes over this locking operation so that the state of FIG. 1 is automatically reached.

The function of the auxiliary pawl 51 can be extended by elongating housing 1 to the right (not shown) so that the carriage 5 can shift so far to the right that when the trigger lever 23 is in its starting position the auxiliary pawl 51 falls behind the righthand end of the second leg 29. When the trigger lever 23 turns to the left, the auxiliary pawl 51 is released so that carriage 5 shifts to the left until the auxiliary pawl 51 engages the recess 55. Thus in this case the switch does not switch.

The further process is as described above, with the trigger lever 23 once turning completely to the left and returning.

This possibility may be useful, for example, when the switch is driven by a clock having one revolution per twelve hours while the switch is to be switched on, for example, after 18 hours. In this case the trigger lever 23 starts to move to the left for the first time after 6 hours and the switch does not switch yet. Only after eighteen hours the trigger lever 23 starts to move to the left from its starting position which results in the switch being switched on.

Sometimes it may be necessary to switch off the switch by hand before this is effected by the trigger lever and after it has been switched on by trigger lever 23 (FIG. 2). To this end the switch-off lever 33 in the embodiment shown is provided with a third leg 57 which can be urged to the right by means of a pin 59 so that the switch-off lever 33 turns counter-clockwise and cam 39 is lifted from the recess 41. The pin 59 is connected to the button 19 which is kept at a distance x (see FIG. 2) from the carriage by a light spring 61. When the button 19 is displaced over the distance x to the right against the force of spring 61, the carriage 5 remains in place because the compression of spring 17 requires considerably more force than that of the light spring 61.

The driving mechanism 27 is shown in a simplified form in FIG. 5 and in a practical embodiment in FIG. 6. It consists of a switching wheel 63 which is urged against an interval disc 69, 71 by a compression spring 67 connected to a chassis plate 65. This interval disc consists preferably of two parallel discs placed on top of each other, one switch-on disc 69 and one switch-off disc 71. The side of the switching wheel 63 facing the interval disc 69, 71 is provided with one or more cams 73 which can co-operate with apertures 75 and 77 in the switch-on disc 69 and the switch-off disc 71, respectively, which apertures together constitute a switching groove 75, 77.

As is shown in FIG. 6 the disc 69, 71 as well as switching wheel 63 are pivotable about a common shaft 79 and the switching wheel may additionally be shifted along the shaft by means of the compression spring 67. The switching wheel 63 is formed as a gear wheel and is driven by a gear wheel 81. The switch-on disc 69 and the switch-off disc 71 are likewise formed as gear wheels and may be rotated by a pinion 87 through intermediate gear wheels 83 and 85. The pinion 87 is rigidly secured to a shaft 89 having an operating knob 91. The shaft 89 is also axially movable so that by depressing and pulling the operating knob 91 the pinion 87 may arbitrarily be caused to mesh with one of the intermediate gear wheels 83 or 85.

The rotations about shaft 79 are in principle possible in one direction only. For the switching wheel 63 this is the direction which corresponds to a displacement to the right in FIG. 5, for the interval disc 69, 71 a displacement to the left. In addition the rotation of the switch-off disc 71 is coupled to that of the switch-on disc 69 because the latter is provided with a carrier 93 which projects in a groove 95 in the switch-off disc 71. As a result the switch-off disc 71 can only be rotated relative to the switch-on disc 69 over an angle which is determined by the length of the groove 95. As a result of this mutual rotation of the two discs the profile of the switching groove 75, 77 varies. The switch-on disc 69 can rotate in an unlimited manner in the given direction and takes along the switch-off disc 71 by means of the carrier 93.

When, starting from the state shown in FIG. 5, the switching wheel 63 moves to the right, the cam 73 engages aperture 75 so that the switching wheel moves along the shaft 79 in the direction of the interval disc 69, 71. The cam 73 bears on the switch-off disc 71 until the switching wheel 69 has been displaced so far to the right that the cam 73 engages the aperture 77 so that the switching wheel again moves along the shaft 79 towards the interval disc 69, 71. In case of further movement to the right of the switching wheel 63 the cam bears on the slope of the apertures 77 and 75 so that the switching wheel gradually moves away from the interval disc. Since the switching wheel 63 is coupled to the first leg 25 of the trigger lever 23 (see FIGS. 1-4) the axial movements of the switching wheel are converted into rotations of the trigger lever.

For a given rotational speed of the switching wheel 63 the time interval between the first and the second axial movement and hence between switching on and switching off of the switch is determined by the position of the discs 69 and 71 relative to each other. In the case shown in FIG. 5 this interval is at a maximum. By displacing the edge of the switch-off disc 71 to the left, the time interval may-be reduced.

In the embodiment of FIG. 6 the gear wheel 81 which drives the switching wheel 63 is in turn driven by a gear wheel 97 which forms part of a clock (not shown) accommodated together with the driving mechanism 27 and the switch (likewise not shown) in a casing 99. The gear wheel 97 may be coupled, for example, to the shaft 79 which is provided with an hour hand 101. and may drive the switching wheel 63 via the gear wheel 81 at a speed of l revolution per 24 hours. A shaft 103 which is provided with a minute hand 105 passes through the shaft 79 which is hollow. Indication discs 107 and 109 may be secured to the switch-on and switch-off discs 69 and 71, which indication discs provide a visible indication of the adjusted time interval through an aperture 111 in the dial 113. Such a device may be used, for example, tocause a recording device for television images (video recorder) to automatically record a television program at a given time of day.

There are of course many modifications of the embodiment described above. Thus, instead of the switching wheel 63 it is alternatively possible to drive the interval disc 69, 71. Alternatively, when the time interval is fixed, the interval disc may be manufactured in one piece. Furthermore the switch need not necessarily be combined with a clock. It may be used whenever a switch-on and switch-off operation is to be consecutively carried out by means of two consecutive movements of a driving mechanism in the same direction, particularly when the return movement of the driving mechanism must not result in the same switching operations in reverse order. An example thereof is the safeguard of high-vacuum installations employing singlebutton operation in which a given operation such as rough vacuum pumping of a vacuum bell jar can only take place if the bell jar has communicated with the atmosphere. A valve between the pre-vacuum duct and the bell jar may then be opened and closed by means of the switch. Tensioning of the switch corresponding to depression of knob 19 in FIG. 3 may then be autornatically effected in the position of the operating knob at which the bell jar is opened to the atmosphere.

What is claimed is:

l. A switch which may be switched on and off with the aid of a switch-on spring and a switch-off spring, respectively, which springs can both be tensioned and locked in the tensioned state in one movement, and an intermediate piece being provided which can be moved by the switch-on spring while the switch-off spring remains tensioned, wherein said intermediate piece comprises a carriage adapted to reciprocate in a housing having fixed switching contacts, a slide having movable switching contacts journalled to reciprocate in said carriage, the switch-on spring acting on the housing and the carriage, and the switch-off spring acting on the carriage and the slide, a trigger mechanism journalled in the housing for unlocking said springs, said trigger mechanism being movable in at least two consecutive stages in the same direction, and locking mechanism carried by said housing for locking said switch-on spring and said switch-off spring in the tensioned condition, said trigger mechanism engaging said locking mechanism for locking said switch-on spring thereby causing unlocking of the switch-on spring during the first stage so that the carriage carrying said slide shifts relative to the housing, and said trigger mechanism engaging said locking mechanism of said switch-off spring to thereby cause unlocking the switch-off spring during the second stage so that the slide shifts relative to the carriage.

2. A switch which may be switched on and off with the aid of a switch-on spring and a switch-off spring, respectively, which springs can both be tensioned and locked in the tensioned state in one movement, and an intermediate piece being provided which can be moved by the switch-on spring while the switch-off spring remains tensioned, wherein said intermediate piece comprises a carriage adapted to reciprocate in a housing having fixed switching contacts, a slide having movable switching contacts jornalled to reciprocate in said carriage, the switch-on spring acting on the housing and the carriage, and the switch-off spring acting on the carriage and the slide, said springs being unlocked with the aid of a trigger mechanism journalled in the housing and being movable in at least two consecutive stages into the same direction, said trigger mechanism unlocking the switch-on spring during the first stage so that the carriage, taking along the slide, shifts relative to the housing, and unlocking the switch-off spring during the second stage so that the slide shifts relative to the carriage, the locking mechanism for the switch-off spring comprising a switch-off lever journalled in the carriage, and at least two legs the first leg of which cooperates with a recess in the slide for the purpose of locking, while the second leg is arranged for cooperation with the trigger mechanism for the purpose of unlocking.

3. A switch as claimed in claim 2, further comprising a cam on the first leg of the switch-off lever, said cam being urged in the recess during locking by means of a spring provided between the carriage and the second leg of the switch-off lever.

4. A switch as claimed in claim 2 wherein said locking mechanism for the switch-on spring comprises a switch-on pawl journalled in the carriage, said pawl being arranged for engagement in a groove in a component of the trigger mechanism for the purpose of locking.

5. A switch as claimed in claim 4, further comprising an auxiliary pawl journalled in the carriage, which pawl engages a groove in the housing if the springs are tensioned while the trigger mechanism is in a position in which locking by means of the switch-on lever does not occur and thereby locks the switch-on spring until the trigger mechanism can take over the locking operation.

6. A switch as claimed in claim 4 wherein said trigger mechanism comprises a trigger lever having three legs the first leg of which is connected to a driving mechanism while the second and third legs are arranged for cooperation with the switch-on pawl and the switchoff lever, respectively.

7. A switch as claimed in claim 6, wherein said driving mechanism comprises a rotating switching wheel which is provided in an axially movable manner on a shaft clamped between a compression spring acting in the axial direction and an interval disc parallel to the switching wheel, the side of said switching wheel facing the interval disc being provided with at least one cam which can co-operate with at least one switching groove in the interval disc, the profile of said switching groove being adapted to the desired axial movement of the switching wheel.

8. A switch as claimed in claim 7, wherein said interval disc comprises a switch-on disc and a switch-off disc coaxially placed against this disc and being adjustable relative to each other by rotation about the said shaft, each disc being provided with at least one aperture which apertures together comprise the said switching groove.

9. A switch as claimed in claim 2 wherein said switchoff lever has a third leg which can be manually moved in such a manner that the switch-off spring is unlocked thereby independently of the position of the trigger mechanism.

10. A switch comprising a housing, a carriage arranged for forward and backward movement within the housing, a plurality of fixed switching contacts carried on said carriage, a slide member journalled in said carriage for reciprocating movement, a plurality of movable switching contacts carried by said slide member, a switch-on spring acting at one end thereof against said housing and the other end thereof acting on said carriage so as to urge said carriage in a direction for causing said movable contacts to engage said fixed switching contacts, a switch-off spring acting at one end thereof against said carriage the other end thereof acting on said slide member so as to urge said slide member in a direction for causing said movable contacts to move away from and disengage said fixed contacts, means carried on said housing for locking said switch-on spring and means for locking said switch-off spring in the tensioned condition, and a trigger mechanism journalled in said housing for movement in at least two consecutive steps in the same direction and engaging said means for locking said springs in the tensioned position, said switch-on spring being unlocked upon the first step of said trigger mechanism so that said carriage carrying said slide member will be moved so that said movable contacts will engage said fixed contacts, said switch-off spring being unlocked upon the second step of said trigger mechanism so that said slide member will be moved to disengage said movable contacts from said fixed contacts.

11. The switch according to claim 10 wherein said means for locking and unlocking said switch-off spring comprises a switch-off lever journalled in said carriage for rotational movement, said lever having first and second legs, said first leg arranged for cooperation with a recess in said slide member so that when said first leg is engaged in said recess said switch-off spring will be locked in the tensioned position, and said second leg arranged for cooperation with said trigger mechanism so that when said second leg is engaged by said trigger mechanism said switch-off lever will be caused to rotate thus unlocking said switch-off spring.

12. The switch according to claim 11 further comprising a cam carried on said first leg of said switch-off lever, and a spring attached at one end thereof to said carriage and at the other end thereof to said second leg of said switch-off lever for urging said cam into engagement with said recess on said slide member when said switch-off spring is in the locked position.

13. The switch according to claim 10 wherein said means for locking said switch-on spring in the tensioned condition comprises a switch-on pawl journalled in said carriage for pivotal movement, and a groove provided in a portion of said trigger mechanism for accommodating said pawl, said switch-on spring being locked in the tensioned condition when said pawl is engaged in said groove.

14. The switch according to claim 13 further comprising an auxiliary pawl journalled for pivotal movement in said carriage, and a groove provided in said housing, said auxiliary pawl arranged for engagement with said groove in the housing when said springs are in the tensioned condition and while said trigger mechanism is in a position for unlocking said switch-on lever for releasing said switch-on spring, whereby said switch-on spring will be maintained in the locked tensioned condition by said auxiliary pawl until said trigger mechanism is in the position for locking said switch on spring.

15. The switch according to claim 13 wherein said trigger mechanism comprises a trigger lever having first, second and third legs, said first leg thereof being connected to a driving mechanism for causing said trigger mechanism to move consecutively through said two steps in the same direction, said second leg thereof being arranged for cooperation with said switch-on pawl, and said third leg thereof being arranged for cooperation for said switch-off lever.

16. The switch according to claim 15, wherein said driving mechanism comprises a switching wheel rotatably carried on a shaft and arranged for axially movement thereon, an interval disc arranged parallel to said switching wheel carried by said shaft, a compression spring acting in the axially direction along said shaft for clamping said switching wheel between said spring and said interval disc, at least one cam member provided on that face of the switching wheel facing the interval disc, at least one switching groove arranged on the face of the interval disc for cooperation with said cam member, the profile of said switching groove being adapted to the desired axially movement of the switching wheel.

17. The switch according to claim 16 wherein said interval disc comprises a switch-on disc and a switchoff disc coaxially arranged and adjustable relative to each other for rotation about said shaft, each disc being provided with at least one aperture comprising said switching groove.

18. The switch according to claim 11 wherein said switch-off lever further comprises a third leg and manually movable means for engagement with said third leg for causing said switch-off lever to be disengaged from the recess in said slide thereby unlocking said switchoff spring independent of the position of said trigger mechanism. 

1. A switch which may be switched on and off with the aid of a switch-on spring and a switch-off spring, respectively, which springs can both be tensioned and locked in the tensioned state in one movement, and an intermediate piece being provided which can be moved by the switch-on spring while the switch-off spring remains tensioned, wherein said intermediate piece comprises a carriage adapted to reciprocate in a housing having fixed switching contacts, a slide having movable switching contacts journalled to reciprocate in said carriage, the switch-on spring acting on the housing and the carriage, and the switch-off spring acting on the carriage and the slide, a trigger mechanism journalled in the housing for unlocking said springs, said trigger mechanism being movable in at least two consecutive stages in the same direction, and locking mechanism carried by said housing for locking said switch-on spring and said switchoff spring in the tensioned condition, said trigger mechanism engaging said locking mechanism for locking said switch-on spring thereby causing unlocking of the switch-on spring during the first stage so that the carriage carrying said slide shifts relative to the housing, and said trigger mechanism engaging said locking mechanism of said switch-off sprinG to thereby cause unlocking the switch-off spring during the second stage so that the slide shifts relative to the carriage.
 2. A switch which may be switched on and off with the aid of a switch-on spring and a switch-off spring, respectively, which springs can both be tensioned and locked in the tensioned state in one movement, and an intermediate piece being provided which can be moved by the switch-on spring while the switch-off spring remains tensioned, wherein said intermediate piece comprises a carriage adapted to reciprocate in a housing having fixed switching contacts, a slide having movable switching contacts jornalled to reciprocate in said carriage, the switch-on spring acting on the housing and the carriage, and the switch-off spring acting on the carriage and the slide, said springs being unlocked with the aid of a trigger mechanism journalled in the housing and being movable in at least two consecutive stages into the same direction, said trigger mechanism unlocking the switch-on spring during the first stage so that the carriage, taking along the slide, shifts relative to the housing, and unlocking the switch-off spring during the second stage so that the slide shifts relative to the carriage, the locking mechanism for the switch-off spring comprising a switch-off lever journalled in the carriage, and at least two legs the first leg of which cooperates with a recess in the slide for the purpose of locking, while the second leg is arranged for cooperation with the trigger mechanism for the purpose of unlocking.
 3. A switch as claimed in claim 2, further comprising a cam on the first leg of the switch-off lever, said cam being urged in the recess during locking by means of a spring provided between the carriage and the second leg of the switch-off lever.
 4. A switch as claimed in claim 2 wherein said locking mechanism for the switch-on spring comprises a switch-on pawl journalled in the carriage, said pawl being arranged for engagement in a groove in a component of the trigger mechanism for the purpose of locking.
 5. A switch as claimed in claim 4, further comprising an auxiliary pawl journalled in the carriage, which pawl engages a groove in the housing if the springs are tensioned while the trigger mechanism is in a position in which locking by means of the switch-on lever does not occur and thereby locks the switch-on spring until the trigger mechanism can take over the locking operation.
 6. A switch as claimed in claim 4 wherein said trigger mechanism comprises a trigger lever having three legs the first leg of which is connected to a driving mechanism while the second and third legs are arranged for cooperation with the switch-on pawl and the switch-off lever, respectively.
 7. A switch as claimed in claim 6, wherein said driving mechanism comprises a rotating switching wheel which is provided in an axially movable manner on a shaft clamped between a compression spring acting in the axial direction and an interval disc parallel to the switching wheel, the side of said switching wheel facing the interval disc being provided with at least one cam which can co-operate with at least one switching groove in the interval disc, the profile of said switching groove being adapted to the desired axial movement of the switching wheel.
 8. A switch as claimed in claim 7, wherein said interval disc comprises a switch-on disc and a switch-off disc coaxially placed against this disc and being adjustable relative to each other by rotation about the said shaft, each disc being provided with at least one aperture which apertures together comprise the said switching groove.
 9. A switch as claimed in claim 2 wherein said switch-off lever has a third leg which can be manually moved in such a manner that the switch-off spring is unlocked thereby independently of the position of the trigger mechanism.
 10. A switch comprising a housing, a carriage arranged for forward and backward movement within the housing, a plurality of fixed switching contacts carrieD on said carriage, a slide member journalled in said carriage for reciprocating movement, a plurality of movable switching contacts carried by said slide member, a switch-on spring acting at one end thereof against said housing and the other end thereof acting on said carriage so as to urge said carriage in a direction for causing said movable contacts to engage said fixed switching contacts, a switch-off spring acting at one end thereof against said carriage the other end thereof acting on said slide member so as to urge said slide member in a direction for causing said movable contacts to move away from and disengage said fixed contacts, means carried on said housing for locking said switch-on spring and means for locking said switch-off spring in the tensioned condition, and a trigger mechanism journalled in said housing for movement in at least two consecutive steps in the same direction and engaging said means for locking said springs in the tensioned position, said switch-on spring being unlocked upon the first step of said trigger mechanism so that said carriage carrying said slide member will be moved so that said movable contacts will engage said fixed contacts, said switch-off spring being unlocked upon the second step of said trigger mechanism so that said slide member will be moved to disengage said movable contacts from said fixed contacts.
 11. The switch according to claim 10 wherein said means for locking and unlocking said switch-off spring comprises a switch-off lever journalled in said carriage for rotational movement, said lever having first and second legs, said first leg arranged for cooperation with a recess in said slide member so that when said first leg is engaged in said recess said switch-off spring will be locked in the tensioned position, and said second leg arranged for cooperation with said trigger mechanism so that when said second leg is engaged by said trigger mechanism said switch-off lever will be caused to rotate thus unlocking said switch-off spring.
 12. The switch according to claim 11 further comprising a cam carried on said first leg of said switch-off lever, and a spring attached at one end thereof to said carriage and at the other end thereof to said second leg of said switch-off lever for urging said cam into engagement with said recess on said slide member when said switch-off spring is in the locked position.
 13. The switch according to claim 10 wherein said means for locking said switch-on spring in the tensioned condition comprises a switch-on pawl journalled in said carriage for pivotal movement, and a groove provided in a portion of said trigger mechanism for accommodating said pawl, said switch-on spring being locked in the tensioned condition when said pawl is engaged in said groove.
 14. The switch according to claim 13 further comprising an auxiliary pawl journalled for pivotal movement in said carriage, and a groove provided in said housing, said auxiliary pawl arranged for engagement with said groove in the housing when said springs are in the tensioned condition and while said trigger mechanism is in a position for unlocking said switch-on lever for releasing said switch-on spring, whereby said switch-on spring will be maintained in the locked tensioned condition by said auxiliary pawl until said trigger mechanism is in the position for locking said switch on spring.
 15. The switch according to claim 13 wherein said trigger mechanism comprises a trigger lever having first, second and third legs, said first leg thereof being connected to a driving mechanism for causing said trigger mechanism to move consecutively through said two steps in the same direction, said second leg thereof being arranged for cooperation with said switch-on pawl, and said third leg thereof being arranged for cooperation for said switch-off lever.
 16. The switch according to claim 15, wherein said driving mechanism comprises a switching wheel rotatably carried on a shaft and arranged for axially movement thereon, an interval disc arranged parallel tO said switching wheel carried by said shaft, a compression spring acting in the axially direction along said shaft for clamping said switching wheel between said spring and said interval disc, at least one cam member provided on that face of the switching wheel facing the interval disc, at least one switching groove arranged on the face of the interval disc for cooperation with said cam member, the profile of said switching groove being adapted to the desired axially movement of the switching wheel.
 17. The switch according to claim 16 wherein said interval disc comprises a switch-on disc and a switch-off disc coaxially arranged and adjustable relative to each other for rotation about said shaft, each disc being provided with at least one aperture comprising said switching groove.
 18. The switch according to claim 11 wherein said switch-off lever further comprises a third leg and manually movable means for engagement with said third leg for causing said switch-off lever to be disengaged from the recess in said slide thereby unlocking said switch-off spring independent of the position of said trigger mechanism. 